1. Technical Field
This invention relates generally to heavy duty pistons for diesel engine applications, and more particularly to the management of cooling oil in articulated pistons.
2. Related Art
Articulated pistons of conventional construction are often formed with a circumferentially extending cooling gallery in the piston head which is open to the bottom and communicates with one or more oil spray nozzles which extend into the skirt of the piston from below and direct a spray of cooling oil into the cooling gallery as the piston reciprocates in the piston cylinder to provide cooling. Lubrication of the pin bores and wrist pin are usually taken care of by internal oil porting. Any cooling of the pin bores and wrist pin are derived from the lubricating oil. In some applications, the pin bosses, their pin bores, bushings and wrist pin can be heated above desired temperatures which can impair the performance and longevity of the piston.
A piston assembly constructed according to the invention includes a piston head having an open bottom cooling gallery formed in a bottom surface of the piston head, a pair of pin bosses depending from the piston head and having pin bores for supporting a wrist pin of a connecting rod, a piston skirt coupled to the pin bosses for reciprocal movement with the piston head, and a stationary oil spray nozzle extending into the piston skirt and having an outlet position for directing a flow of cooling oil along a path toward the cooling gallery. An oil deflector shield is carried by the piston skirt in position to substantially obstruct the flow of cooling oil to the cooling gallery and to direct the obstructed flow onto the pin bosses when the piston head is moved to a lowered position. The oil deflector shield is positioned also to move substantially out of the path of the cooling oil to cause the cooling oil to be directed into the cooling gallery when the piston head is moved to a raised position.
The invention also contemplates a method of cooling a reciprocating piston which employs the mentioned deflector shield which operates to selectively obstruct the flow of cooling oil to the cooling gallery when the piston is at the bottom of stroke position in order to attain, during a portion of the piston stroke, direct cooling of the pin bore regions of the piston. This invention has the advantage of providing direct cooling to the cooling gallery of the piston head at times during the stroke of the piston when cooling of the head is needed most, namely when the piston is toward the top of stroke position where it sees the most heat and thus requires the most cooling. As the piston travels toward the bottom of stroke position, the piston head is moved away from the heat of combustion so as to lessen the cooling requirements and, according to the invention, the deflector is operative during this time to redirect the cooling oil onto the pin boss regions so that the pin boss regions are directly cooled at a time during the piston cycle when the cooling of the head is less critical.
The invention thus has the advantage of providing direct cooling of the pin boss regions without impairing the efficient cooling of the piston head.
The invention has the further advantage of achieving cooling of the piston head and pin bores with use of a single oil spray nozzle in conjunction with the deflector.